1. Field of the Invention
The present invention relates generally to a method and system for processing a voice call in a communication system, and, in particular, to a method and system for processing a voice call in a communication system that manages heterogeneous networks.
2. Description of the Related Art
With the rapid progress of the mobile communication and Internet technologies targeted to meet various needs of the subscribers, the recent mobile communication services have reached the phase of providing not only the existing voice call services but also the high-speed packet data services capable of transmitting high-capacity digital data as well as E-mail and still images via a mobile terminal. Accordingly, the mobile communication systems are evolving from the voice-based Circuit Switched (CS) domain into the packet-based Packet Switched (PS) domain.
The Core Network (CN) that provides multimedia services over the Internet has changed from the existing circuit-based CN into the packet-based CN, and is now evolving into an Internet Protocol (IP)-based CN. A communication system that provides IP Multimedia services (IM services) to the subscribers over the IP-based CN is called an IMS, and third Generation Partnership Project (3GPP)/3GPP2 is conducting various researches to smoothly provide ALL IP services over the IMS.
The IMS is composed of a set of signaling and bearers related to the network elements, and should be able to approach the web-based technology for audio, video and message data, and wireless subscribers. Because the IMS provides various types of packet data services based on an IP transport protocol, the IMS users can exchange multimedia-type contents, such as picture, video clip and sound clip, with each other over Session Based Messages.
The mobile communication systems are now developing into the heterogeneous communication systems that manage heterogeneous networks such as the CS domain and PS domain networks in an integrated way. Herein, the ‘PS domain’ is also called an ‘IMS domain’ and the two terms are used interchangeably.
Describing voice call processing in the heterogeneous communication system, Voice Call Continuity (VCC) supports both terminating domain selection between the CS domain and the IMS domain, and IMS-to-CS and CS-to-IMS domain transfer. To this end, all calls of the VCC subscriber are anchored in a VCC Application Server (AS). Therefore, a terminating CS call is anchored in the VCC AS after being rerouted to the IMS domain. All terminating calls incoming from the external network are input to the IMS network via a Media Gateway Control Function (MGCF), and then transmitted to the selected terminating domain via the VCC AS.
Generally, in the heterogeneous communication system, the CS domain and the IMS domain are different in their service providers. Therefore, when the user uses the subscriber identification number, or Mobile Station ISDN Number (MSISDN), that is used in the CS domain, even in the IMS domain, all voice calls are rerouted to the IMS domain after terminating at the CS domain. That is, the IMS domain anchors the corresponding call in the VCC AS, and the VCC AS selects a terminating domain and reroutes the call to the corresponding terminating domain, which unnecessarily performing many procedures.